There is an urgent need to find new, sustainable protein and lipid sources for aquafeeds which are not in direct competition with existing food production value chains and human nutrition. Aquaculture farming entails discharges of large volumes of waste products, ascribed as fish sludge, which consist of feed spill, respiratory products and faeces. Utilizing fish sludge in the circular bioeconomy to feed low‐trophic species such as marine polychaetes and insects may provide a sustainable feed chain, however, food security must not compromise feed or food safety, and the use of fish sludge as feed is currently not permitted in the European Union. Integration of fish sludge in the circular bioeconomy requires knowledge of potential chemical and biological risks involved.
The SecureFeed project has investigated the fate of different biological and chemical hazards in fish sludge and their potential fate via ingestion by invertebrates . To test the potential of the polychaete Hediste diversicolor and black soldier fly Hermetia illucens larvae (BSFL) to bioaccumulate, sustain or expunge known fish pathogens and heavy metals, two 2-week long feeding experiments were conducted during which the animals were fed on a standardised aquaculture sludge mix spiked with different concentrations of two different viruses and two different bacteria. Moreover, juvenile polychaetes and BSFL were exposed with prions from brain homogenates of scrapie-positive sheep, mixed or not mixed with aquaculture sludge , to assess, for the first time, whether H. diversicolor and H. illucens can serve as potential vectors for prion diseases.
None of the viruses or bacteria could be detected in the polychaetes or BSFL after 14 days of exposure. Polychaetes did not accumulate heavy metals from the aquaculture sludge exceeding levels set by current EU regulations for animal feed ingredients , while BSF larvae bio accumulated some undesirable substances including Cd, Hg and dioxins . Polychaetes and BSFL orally inoculated with a substantial dose of prions retained detectable levels of prions using the ultrasensitive amplification method (PMCA) indicating that these organisms can potentially serve as mechanical vectors for prion diseases.
This work was funded by a grant from FHF – Norwegian Seafood Research Fund (“SecureFeed”, grant no. #901732). The prion experiments were carried out at the Norwegian Veterinary Institute (Norwegian National reference laboratory for TSE in animals, WOAH Reference laboratory for CWD, Ås, Norway), SINTEF Ocean’s national research infrastructure “Norwegian Center for Plankton Technology (#245937/F50)” and at IMR’s ISO-certified laboratories (NS-EN ISO/IEC 17025). The authors thank Protix for supplying BSFL for the experiments and Dr Olivier Andreoletti from INRAe / ENVT Toulouse, France, for kindly providing us with brain tissues from sheep naturally infected with scrapie.